Pumping Unit Having Zero-Imbalanced Beam, Lagging Counterweights, and Setback Crank Point

ABSTRACT

A surface unit can operate as a longer stroke unit to reciprocate a rod string for a downhole pump in a well. The unit has an end weight that gives the walking beam and head a zero-imbalance about the unit&#39;s fulcrum point. The unit can also operate as a phased unit in which the counterweights of the crank arms lag behind the pivot connection and/or the crank point is disposed rearward of the equalizer bearing of the walking beam.

BACKGROUND OF THE DISCLOSURE

Reciprocating pump systems, such as sucker rod pump systems, extractfluids from a well and employ a downhole pump connected to a drivingsource at the surface. A rod string connects the surface driving forceto the downhole pump in the well. When operated, the driving sourcecyclically raises and lowers the downhole pump, and with each stroke,the downhole pump lifts well fluids toward the surface.

For example, FIG. 1 shows a sucker rod pump system 10 used to producefluid from a well. A downhole pump 14 has a barrel 16 with a standingvalve 24 located at the bottom. The standing valve 24 allows fluid toenter from the wellbore, but does not allow the fluid to leave. Insidethe pump barrel 16, a plunger 20 has a traveling valve 22 located at thetop. The traveling valve 22 allows fluid to move from below the plunger20 to the production tubing 18 above, but does not allow fluid to returnfrom the tubing 18 to the pump barrel 16 below the plunger 20. A drivingsource (e.g., a pump jack or pumping unit 30) at the surface connects bya rod string 12 to the plunger 20 and moves the plunger 20 up and downcyclically in upstrokes and downstrokes.

During the upstroke, the traveling valve 22 is closed, and any fluidabove the plunger 20 in the production tubing 18 is lifted towards thesurface. Meanwhile, the standing valve 24 opens and allows fluid toenter the pump barrel 16 from the wellbore.

At the top of stroke, the standing valve 24 closes and holds in thefluid that has entered the pump barrel 16. Furthermore, throughout theupstroke, the weight of the fluid in the production tubing 18 issupported by the traveling valve 22 in the plunger 20 and, therefore,also by the rod string 12, which causes the rod string 12 to stretch.During the downstroke, the traveling valve opens, which results in arapid decrease in the load on the rod string 12. The movement of theplunger 20 from a transfer point to the bottom of stroke is known as the“fluid stroke” and is a measure of the amount of fluid lifted by thepump 14 on each stroke.

At the surface, the pump jack 30 is driven by a prime mover 40, such asan electric motor or internal combustion engine, mounted on a pedestalabove a base 32. Typically, a pump controller 60 monitors, controls, andrecords the pump unit's operation. Structurally, a Samson post 34 on thebase 32 provides a fulcrum on which a walking beam 50 is pivotallysupported by a saddle bearing assembly 35.

Output from the motor 40 is transmitted to a gearbox 42, which provideslow-speed, high-torque rotation of a crankshaft 43. Both ends of thecrankshaft 43 rotate crank arms 44 having counterbalance weights 46.Each crank arm 44 is pivotally connected to a pitman arm 48 by a crankpin bearing 45. In turn, the two pitman arms 48 are connected to anequalizer bar 49, which is pivotally connected to the rear end of thewalking beam 50 by an equalizer bearing assembly 55.

A horsehead 52 with an arcuate forward face 54 is mounted to the forwardend of the walking beam 50. As is typical, the face 54 may have tracksor grooves for carrying a flexible wire rope bridle 56. At its lowerend, the bridle 56 terminates with a carrier bar 58, upon which apolished rod 15 is suspended. The polished rod 15 extends through apacking gland or stuffing box at the wellhead 13. The rod string 12 ofsucker rods hangs from the polished rod 15 within the tubing string 18located within the well casing and extends to the downhole pump 14.

As is known, pump jack operating characteristics are typicallycharacterized by the American Petroleum Institute (“API”)Specifications, which expresses parameters as a function of the geometryof a pumping unit's four-bar linkage. Standardized API linkage geometrydesignates: dimension “A” as the distance from the center of the saddlebearing 35 to the centerline of the polished rod 15; dimension “C” asthe distance from the center of the saddle bearing 35 to the center ofthe equalizer bearing 55; dimension “P” as the effective length of thepitman arm 48 as measured from the center of the equalizer bearing 55 tothe center of the crank pin bearing 45; dimension “R” as the distancefrom the centerline 43 of the crankshaft to the center of the crank pinbearing 45; dimension “H” as the height from the center of the saddlebearing 35 to the bottom of the pump jack base 32; dimension “I” is thehorizontal distance from the center of the saddle bearing 25 to thecenterline 43 of the crankshaft; dimension “G” as the height from thecenterline 43 of the crankshaft to the bottom of the pump jack base 32;and dimension “K” as the distance from the centerline 43 of thecrankshaft to the center of the saddle bearing 35. Dimension “K” may becomputed as:

K=√{square root over ((H−G)²+l²)}

Alteration of the four-bar linkage may have a significant effect on theoperating characteristics of the pumping unit 30, such as changing theallowable polished rod load, changing the shape of the permissible loadenvelope, altering the length of the pumping stroke, inducing a phaseangle shift in the counterbalance, etc. Moreover, the change inoperating characteristics at surface may further affect controls,analysis, and diagnostics of the downhole rod pump because calculationsfor these features are typically based on the standard four-bar linkage(K-R-P-C).

A conventional rod pumping unit 10 as in FIG. 1 has considerable inertiaeffects inherent to the design. The crank arms 42 connected to the gearreducer 42 and having the counterweights 46 affixed to them mustovercome the equivalent torque that is applied by the connected rodstring 12 extending from the wellbore to the horsehead 52. Thesecounterweights 46 are significantly large masses (˜1,800 lb. for amid-range counterweight) so a considerable amount of torque from theprime mover 40 is needed to initiate their rotational motion.Additionally, the balance beam 50 and associated parts that convert therotary motion of the crank arms 42 into articulating motion also havesignificant mass that also require torque from the prime mover 40 tosustain the desired rocking motion that lifts and lowers the rod string12. Even though the conventional rod pumping unit 10 has been in use forover 80 years, some of the inertia effects of both the rotational andarticulating elements are not as well-known as some might believe.

There are some pumping unit designs that are different than theconventional pumping unit 10 of FIG. 1. For example, it has been knownfor some time in the art to place weight at the rearward end of awalking beam for a surface pumping unit. As two examples, U.S. Pat. Nos.2,175,588 and 2,408,200 have additional weight on the rearward end ofthe walking beam. The rearward end of the beam extends a considerabledistance beyond the point of attachment of the pitman arms and isprovided with a weight for counterbalancing the pumping loads.

Another type of pumping unit having a weight on the rearward end of thebeam is a beam balanced unit. As opposed to a crank balanced unit as inFIG. 1, this type of beam balanced unit does not use counterweights oncrank arms. Instead, the beam balanced unit only uses counterweight onthe rearward end of the beam. Typically, the weight is adjustable sooperators can determine the proper number or placement of weight toachieve the desired counterbalance. Such a beam balance unit has beenused for low production installations, such as for producing a shallowwell in a mature oilfield.

A curved beam pumping unit available from Schlumberger uses anadjustable weight positioned on the bent beam's rearward end. Theconventional crank weight and the adjustable beam weight on the curvedbeam are intended to benefit the gearbox torque of this curved beampumping unit.

The subject matter of the present disclosure is directed to overcoming,or at least reducing the effects of, one or more of the problems setforth above.

SUMMARY OF THE DISCLOSURE

According to one arrangement of the present disclosure, a surfacepumping unit is operated by a prime mover for reciprocating a rod loadfor a downhole pump in a well. The unit comprises a frame, a beam, acrank arm, a counterweight, and a pitman art.

The frame is disposed at surface and has a fulcrum point. The beam ispivotable at the fulcrum point of the frame. The beam has a first endhaving a head connecting to the rod load extending from the well. Thebeam has a second end having a first bearing point. An end weight isdisposed on the second end of the beam rearward of the first bearingpoint. A forward section of the first end of the beam and the headdisposed forward of the fulcrum point has a forward weight. A rearwardsection of the second end of the beam and the end weight disposedrearward of the fulcrum point having a rearward weight. The forwardweight is balanced relative to the rearward weight.

The crank arm is connected to the prime mover and is rotatable therebyabout a crank point. The counterweight is disposed on the crankarm, andthe pitman arm is connected between the first bearing point on the beamand a second bearing point on the crank arm. The second bearing point isdisposed between the counterweight and the crank point.

The crank arm rotated by the prime mover about the crank pointtranslates the pitman arm to oscillate the beam on the fulcrum point andreciprocates the rod load along the wellbore axis.

The frame can include: a base disposed at the surface; and a postextending from the base to the fulcrum point along a line from vertical.

The beam can define a straight axis having first and second sections.The first section from the fulcrum point to a face of the head can havea first length (A), and the second section from the fulcrum point to thefirst bearing point can have a second length (C). The first length (A)can be greater than the second length (C).

The fulcrum point can comprise a saddle bearing, the first bearing pointcan comprise an equalizer bearing, and the second bearing point cancomprise a crank pin bearing. The unit can include another crank armconnected to the prime mover and rotatable thereby about another crankpoint; and another pitman arm connected between another first bearingpoint on the beam and another second bearing point on the other crankarm, wherein the pitman arms connect with an equalizer beam at the firstbearing point. The unit can further comprise a gear reducer operablyconnecting the crank point to the prime mover.

In one configuration, the crank point can be centered vertically belowthe first bearing point on the beam when the beam is situatedhorizontally. For instance, the first bearing point can be disposed at afirst horizontal dimension (C) along the beam relative to the fulcrumpoint, and the crank point can be disposed at a second horizontaldimension (I) relative to the fulcrum point. In this configuration, thesecond horizontal dimension (I) can be approximately equal to the firsthorizontal dimension (C).

For this configuration, the second bearing point can be disposed along alongitudinal axis defined by the crank arm. Alternatively, the secondbearing point can be disposed offset at an angle from the longitudinalaxis of the crank arm.

In another configuration, the crank point can be situated verticallyrearward below the first bearing point on the beam when the beam issituated horizontally. For instance, the first bearing point can bedisposed at a first horizontal dimension (C) along the beam relative tothe fulcrum point, and the crank point can be disposed at a secondhorizontal dimension (I) relative to the fulcrum point. The secondhorizontal dimension (I) can be greater than the first horizontaldimension (C).

For this other configuration, the second bearing point can be disposedalong a longitudinal axis defined by the crank arm. Alternatively, thesecond bearing point can be disposed offset at an angle from thelongitudinal axis of the crank arm.

According to another arrangement of the present disclosure, a surfacepumping unit is operated by a prime mover for reciprocating a rod loadfor a downhole pump in a well. The unit comprises a frame, a beam, acrank arm, a counterweight, and a pitman arm. The frame is disposed atthe surface and has a fulcrum point. The beam is pivotable at thefulcrum point of the frame. A first end of the beam has a headconnecting to the rod load extending from the well. A second end of thebeam has a first bearing point and has an end weight disposed rearwardof the first bearing point.

The crank arm is connected to the prime mover and is rotatable therebyabout a crank point. The counterweight is disposed on the crankarm. Thepitman arm is connected between the first bearing point on the beam anda second bearing point on the crank arm. The second bearing point isdisposed between the counterweight and the crank point and is disposedoffset at an angle from a longitudinal axis defined by the crank arm.

A forward section of the first end of the beam and the head disposedforward of the pivot point can have a forward weight. Meanwhile, arearward section of the second end of the beam and the end weightdisposed rearward of the pivot point can have a rearward weight, wherethe forward weight is balanced relative to the rearward weight about thepivot point.

The crank point can be situated vertically rearward below the firstbearing point on the beam when the beam is situated horizontally. Inthis instance, the first bearing point can be disposed at a firsthorizontal dimension (C) along the beam relative to the fulcrum point,and the crank point can be disposed at a second horizontal dimension (I)relative to the fulcrum point, where the second horizontal dimension (I)can be greater than the first horizontal dimension (C).

This other arrangement of the pumping unit can include any of theadditional features described above with reference to the previousarrangement.

According to yet another arrangement of the present disclosure, areciprocating pump system is used for a well. The system comprises adownhole pump disposed in the well and comprises a pumping unit disposedat the surface and coupled to the downhole pump by a rod string. Thepumping unit can include any of the various features of the pumpingunits described above.

The foregoing summary is not intended to summarize each potentialembodiment or every aspect of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a reciprocating rod pump system knownin the art.

FIG. 2A illustrates an elevational view of a reciprocating rod pumpsystem of the present disclosure.

FIG. 2B illustrates geometry of the disclosed reciprocating rod pumpsystem.

FIG. 3A illustrates an elevational view of another reciprocating rodpump system of the present disclosure.

FIG. 3B illustrates geometry of the disclosed reciprocating rod pumpsystem.

FIG. 3C illustrates another geometry of the disclosed reciprocating rodpump system.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 2A, a surface pumping unit 100 according to thepresent disclosure is used for reciprocating a rod string for a downholepump in a well. Details of the well, wellhead, polished rod, carrierbar, downhole pump, and the like are not shown here for simplicity, buthave been discussed previously.

The pumping unit 100 includes a frame having a base 110 and a Samsonpost 112. An actuator or prime mover 120 is disposed on the base 110, acrank assembly is connected to the prime mover 120, and a walking beam150 is connected to the crank assembly and is supported by the Samsonposts 112 on the base 110. Structurally, the Samson posts 112 on thebase 110 provide a fulcrum point on which the walking beam 150 ispivotally supported by a saddle bearing assembly 116. In addition to theSamson posts 112, the frame on the base 110 may include one or more backposts 114 joined together forming an A-frame to support the walking beam150.

The pumping unit 100 is driven by the prime mover 120, such as anelectric motor or internal combustion engine, mounted on a pedestalabove the base 110. A pump controller (not shown) monitors, controls,and records the pump unit's operation. Output from the prime mover 120is transmitted to a gearbox 124, which provides low-speed, high-torquerotation of a crankshaft 132. Both ends of the crankshaft 132 rotate arespective crank arm 130 about the crankshaft's centerline. Disposedaway from the crankshaft 132, the crank arms 132 each have acounterbalance weight 136. Each crank arm 130 is pivotally connected toa pitman arm 140 by a crank pin bearing 134, also called a wrist pin. Inturn, the two pitman arms 140 are connected to an equalizer bar 142,which is pivotally connected toward the rear end 151 b of the walkingbeam 150 by an equalizer bearing assembly 156.

A horsehead 152 with an arcuate forward face 154 is mounted to theforward end 151 a of the walking beam 150. As is typical, the face 154may have runners (tracks or grooves) for carrying a flexible wire ropebridle 56. At its lower end, the bridle 56 terminates with a carrier bar(not shown), upon which a polished rod (not shown) for a reciprocatingrod system is suspended. As before, the polished rod typically extendsthrough a packing gland or stuffing box at a wellhead for connection todownhole sucker rods and pump.

As the prime mover 120 rotates the crank arms 130, the walking beam 150seesaws on the frame's bearing 116 so the polished rod reciprocates therod system and downhole pump in the well. During operation, for example,the prime mover 120 and gearbox 124 rotate the crank arms 130, whichcauses the rearward end 151 b of the walking beam 150 to move up anddown through the movement of the pitman arms 140. Up and down movementof the rearward end 151 b causes the walking beam 150 to pivot about thebearing assembly 116 resulting in downstrokes and upstrokes of thehorsehead 152 on the forward end 151 a.

During an upstroke, for example, the prime mover 120 and gearbox 124aided by the counterbalance weights 136 overcomes the weight and load onthe horsehead 152 and pulls the polished rod string up from thewellbore, which reciprocates the rod string and downhole pump in thewell to lift fluid. During a downstroke, the prime mover 120 aided bythe weight and load on the horsehead 154 rotates the crank arms 130 toraise the counterbalance weights 136.

The pumping unit 100 may be used for specific pumping applications,calling for changes in its particular geometry and structure compared toa conventional unit. The unit 100 may also be used in pumpingapplications having particular requirements for rod loads, strokelength, and the like. For example, the unit 100 may have an oversizedhorsehead 152, an increased forward length (A) on the beam 150, or otherchanges to produce longer strokes with the unit 100.

The changes in the geometry and the structure, the changes in theparticular rod loads, or the like can produce imbalance in the unit 100.To offset the imbalance, the unit 100 according to the presentdisclosure has an end weight 160 on the rearward end 151 b of the beam150. The end weight 160 can include a unitary or modular unit and canhave a fixed weight value. The end weight 160 can attach or affix to theend 151 b in a number of ways. For example, the end weight 160 can beattached to the rearward end of the beam 150 using techniques, such aswelding, bolting, flanges, and the like. The attachment may be permanentor may allow for different end weights 160 with different weight valuesto be used interchangeably as needed on the end 151 of the beam 150.

The end weight 160 is configured to eliminate the imbalance of the beam150 and the head 152 and allow the gear reducer 124 and the crank armcounterweights 136 to only have to lift the rod string. Thisconfiguration may allow the pumping unit 100 to pull higher loads than aconventional unit. Moreover, this configuration may allow for easierset-up of the unit 100 due to the zero-imbalance of the beam 150. Forexample, the beam 150 with head 152 and weight 160 can easily beadjusted with little force (inertia) during set up on the frame (112,114), which may eliminate the need for heavier installation equipment.The reduced inertia may also reduce the amount of torque needed from theprime mover 120 to initiate motion and/or to sustain the desired motionthat lifts and lowers the rod string.

Although the configuration can be incorporated into any size of the unit100, the benefits may be best suited for the pumping unit 100 when headheavy, as is typically found in a larger stroke unit. Some installationsrequire pumping units having larger or longer strokes compared toconventional arrangements. The typical stroke length of a conventionalpumping unit may be from about 50-in to about 240-in, whereas the strokelength for a larger stroke, conventional pumping unit installation maybe from about 150-in to 300-in. (Reference to larger stroke here is notmeant to be confused with those “long stroke pumping units” that use abelt drive.)

For the larger stroke pumping units, the length of the walking beamahead of the fulcrum point 116 has to be increased so as to provide thelarger stroke. This results in a longer arm dimension “A” for thedistance from the center of the saddle bearing 116 to the centerline ofthe polished rod. In general, the arm dimension (A) from the fulcrumpoint 116 to the face 154 of the head 152 is greater than the other beamdimension (C) from the fulcrum point 116 to the equalizer bearing point156. For the larger stroke pumping unit 100 disclosed here, the forwarddimension (A) can be about two times longer than the rearward dimension(C), but other variations can be used. In general, the ratio of theforward dimension (A) relative to the rearward dimension (C) can bebetween approximately 0.8 to just over 2 (e.g., about 2.05). In additionto the additional arm length, the longer stroke unit also requires alonger runner for the wire rope bridle so that the head 152 must belarger, which results in more weight. The longer moment arm (A) and headweight create a large structural imbalance in the beam 150.

In the unit 100 having a longer moment arm (A) and an oversizedhorsehead 152 and/or having a significant increase in the imbalance dueto other secondary effects, additional counterweight 136 could be addedto the crank arms 130 to offset the imbalance. Increasing thecounterweight 136 on the crank arms 130 would add to the rotationalinertia effects, which may not be desirable. Instead, the presentarrangement adds the additional weight to the rearward end 151 b of thebeam 150 using the end weight 160. This added weight 160 to the end 151b of the beam 150 changes the articulating inertia effects, which mayhave benefits in some implementations.

In many installations, for example, the prime mover 120 is driven with avariable speed drive. This tends to keep the rotational speed of thegear reducer 124 and the crank arms 130 at nearly a constant rate.Therefore, any rotational inertia effects are reduced considerably andmay be of concern only during start-up and shut-down operations.However, if such a unit were allowed to operate in an out-of-balancecondition, the rotational inertia effects can become more pronounced.The end weight 160 on the end 151 b of the beam 150 opposite thehorsehead 152 to overcome the imbalance will tend to increase thearticulating inertia. However, the beam 150 is supported on (and rotatesabout) the saddle bearing assembly 116, which may tend to reduce the neteffect.

In particular, even though the articulating inertia is increased, therequirement to overcome the imbalance with the counterweights affixed tothe crank arms is reduced. In turn, the net torque required from theprime mover to operate the unit 100 is reduced. Essentially, the addedweight to the end of the walking beam to offset the imbalance increasesthe articulating inertia slightly and reduces the rotational inertia.More significantly, the amount of counterweight torque required isreduced. Example calculations show that the additional weight 160 on theend of the walking beam 150 may reduce the counterweight torque on theorder of about 30%, which is a big savings when it comes to motor powerrequirements. Additionally, the example calculations show that the netinertia effects of the articulating members do not increase enough toraise any other concerns.

Additional features of the pumping unit 100 are discussed with referenceto FIG. 2B, which schematically depicts the geometric arrangement of theunit 100. In this depiction, the frame, actuator, arms, and the like arenot shown. Instead, the fulcrum point for the walking beam 150 isrepresented as a pivot point for the bearing assembly 116.

As shown in the geometry of FIG. 2B, the rearward end 151 b of the beam150 has the bearing point (i.e., equalizer bearing assembly 156) and hasthe additional end weight 160 disposed rearward of the bearing point156. Because the beam 150 is pivotable at the fulcrum point of thesaddle bearing assembly 116 on the frame, a forward section 153 a of theforward end of the beam 150 and the head 152 disposed forward of thepivot point 116 has a forward weight (WF+WH), whereas a rearward section153 b of the rearward end of the beam 150 and the end weight 160disposed rearward of the pivot point 116 has a rearward weight (WR+WE).

For the disclosed pumping unit 100, the forward weight (WF+WH) isintended to be balanced relative to the rearward weight (WF+WE) aboutthe fulcrum point 116. Accordingly, the weight value (WE) for the endweight 160 is selected to achieve this balance by countering anyincreased weight from an increased length (A) of the forward beam endand from an increased size for the head 152 so the pumping unit 150 canbe used for longer stroke applications.

In one implementation, for example, the walking beam 150 has a weight(WF+WR) of about 6,500-lbs, and the head 152 has a weight (WH) of about3500-lbs. The equalizer beam 142 can be about 1,300-lbs. For thisimplementation, the weight value (WE) for the end weight 160 can beabout 6,500-lbs. In this instance, the extra weight value (WE) providedby the end weight 160 can be about ⅓ of the total weight of the assembly(walking beam 150, head 152, equalizer beam 142, and end weight 160). Ofcourse, as one skilled in the art will appreciate with the benefit ofthe present disclosure, the weight value (WE) for the end weight 160will vary depending on the lengths (A) and (C) of the beam 150 and othervariables, dimensions, and weights of elements on the pumping unit 100.

The face 154 connects to the polished rod extending along the wellboreaxis WA from the wellhead. The prime mover (120) is not shown, but thecrank arm (130) is depicted as radius (R) connected between a crankpoint of the crank pin 132 and a first bearing point for the wrist pin134. The pitman arm (140) is depicted as linkage (P) connected betweenthe first bearing point 134 and a second bearing point for the equalizerbearing assembly 152 on the walking beam 150.

The crank point 132 is disposed at a first dimension (K) relative to thefulcrum point 116 (i.e., the distance from the centerline of thecrankshaft to the center of the saddle bearing), and the pitman arm(130) has a length of a second dimension (P) (i.e., the effective lengthof the pitman arm (130) as measured from the center of the equalizerbearing 156 to the center of the crank pin bearing 134). The firstbearing point 134 is disposed at a third dimension (R) from the crankpoint 132 (i.e., the distance from the centerline 132 of the crankshaftto the center of the crank pin bearing 134), and the second bearingpoint 156 is disposed at a fourth dimension (C) relative to the fulcrumpoint 116 (i.e., the distance from the center of the saddle bearing 116to the center of the equalizer bearing 156). This completes the four-barlinkage of the unit 100.

Other geometric measures include the dimension (A), heights (H) and (G),and separation (I). The dimension (A) is the distance from the center ofthe saddle bearing 116 to the centerline of the polished rod representedby the wellbore axis WA and defines the radius at which the face 154arcs along (circumscribes) a segment at a radius relative to the fulcrumpoint 116, the segment being tangential to the wellbore axis (WA). Theheight (H) is the fixed elevation of the fulcrum point 116 from thesurface S on which the base (110) is supported, and the height (G) isthe fixed elevation of the crank point 134 from the surface S. Finally,the separation (I) is the fixed vertical distance between the fulcrumpoint 116 and the crank point 132.

As noted, the unit 100 operates as a kinematic four-bar linkage (KPRC),in which each of four rigid links (KPRC) is pivotally connected to twoother of the four links (KPRC) to form a closed polygon. In themechanism, the link (K) is fixed as the ground link. The two links (C,R) connected to the ground link (K) are referred to as grounded links,and the remaining link (P) not directly connected to the fixed groundlink (K) is referred to as the coupler link. The grounded link (R)rotated by the prime mover about the crank point 132 translates thecoupler link (P) arm to oscillate the grounded link (C) for the beam 150on the fulcrum point 116. This in turn oscillates the radius (A) atwhich the face 154 arcs along (circumscribes) the segment.

Configuring the four-bar linkage (KPRC) of the unit 100 may configurethe operating characteristics of the pumping unit 100, such as definingthe allowable polished rod load, defining the shape of the permissibleload envelope, defining the length of the pumping stroke, inducing aphase angle shift in the counterbalance, etc. Moreover, the configuredoperating characteristics at surface may further defines controls,analysis, and diagnostics of the downhole rod pump because calculationsfor these features are typically based on the four-bar linkage(K-R-P-C).

Arranged for longer stroke applications, the unit 100 may have a forwardbeam dimension (A) that is increased compared to a standard strokepumping unit. The head 152 may also be larger, having an increase weight(WH) and having a face 154 that may define a greater segment compared toa standard stroke pumping unit. However, the end weight 160 on therearward end 151 b of the beam 150 that produces the zero-imbalance ofthe beam 150 can allow the unit 100 to operate efficiently as akinematic four-bar linkage (KPRC) using many of the same or similarcomponents (i.e., prime mover 120, gearbox 124, crank arms 130,counterweights 136, pitman arms 140, and the like) as used for aconventional longer stroke pumping unit. This provides the unit 100 withflexibility to meet the needs of various pumping implementations.

In the present arrangement of FIGS. 2A-2B, the gear reducer 124 operablyconnecting the prime mover 120 to the crankshaft 132 is situated in aconventional manner. In particular, the gear reducer 124 has aslow-speed shaft—i.e., the crankshaft 132 about which the crank arms 130rotate. For this conventionally situated reducer, the center of thisslow-speed crankshaft 132 is situated relative to the unit's fulcrumpoint 116 so that the crankshaft 132 may sit directly under the centerof the equalizer bearing 156. Accordingly, in the arrangement of FIGS.2A-2B, the crank point of the crankshaft 134, which is the slow-movingshaft of the reducer 124, can be centered vertically below the rearwardbearing point (i.e., equalizer bearing 156) on the beam 150 when thebeam 150 is situated horizontally. In other words, the horizontaldistance (I) between the saddle bearing 116 and the crank point 132 maythe same as or approximately close to the horizontal distance (C)between the saddle bearing 116 and the equalizing bearing 156.

The values of these horizontal distances (I) and (C) depend on theparticulars of the implementation, such as the other dimensions (e.g.,KPRAGH) of the unit 100, rod loads, counterweight values, etc. Ingeneral, the horizontal distances (I) and (C) can be approximately equalwith the difference being approximately between 0 to 10%. In fact, thehorizontal distances (I) can be equal to about the distance from thefulcrum point 116 to the end 151 b of the beam 150, which is typicallyabout 9% greater than the distance (C). Such an arrangement dictatessome of the other dimensions for the interconnected links (KPRC) of theunit 100.

Additionally, the cranks' bearing point or wrist pin 134 on the crankarm 130 is disposed on the arm's longitudinal axis 131, as seen in FIG.2B. In particular, the crankpin holes in the pumping unit 100 runparallel to the longitudinal axis 131 of the crank arm 130. Therefore,the counterweights 136 on the crank arms 130 do not lag relative to thepivot connection (wrist pins 134) between the crank arms 130 and thepitman arms 140 as the crank arms 130 rotate clockwise. The pumping unit100 could run either clockwise or counterclockwise.

The arrangement of the various elements of the disclosed unit 100 ispreferably configured so that the pitman arms (140) operate in tension.The counterbalance weight 136 is selected based on the weight and loadof the reciprocating rod system (i.e., the force required to lift thereciprocating rod and fluid above the downhole pump in the wellbore). Inone embodiment, the counterbalance weight 136 may be selected so thatone or more components of the pumping unit 100 have substantiallysymmetrical acceleration and/or velocity during upstrokes anddownstrokes. The component may be any moving part of the pumping unit100, such as the pitman arm 140, the wrist pin assembly 134, the crankarm 130, the equalizer beam 142, the walking beam 150, the horsehead152, etc.

Turning to FIG. 3A, another arrangement of a pumping unit 100 isillustrated. Many features of this pumping unit 100 are similar to thosediscussed previously. Again, the surface pumping unit 100 is operated bya prime mover 120 for reciprocating a rod load for a downhole pump in awell. The unit 100 includes a frame 112, 114, a beam 150, a crank arm130, a counterweight 136, and a pitman arm 140. The frame 112, 114 isdisposed at the surface and has a fulcrum point 116, about which thebeam 150 is pivotable at a pivot point. A forward end 151 a of the beam150 has a head 152 connecting to the rod load extending from the well.The second or rearward end 151 b has a first bearing point 156 and hasan end weight 160 disposed rearward of the first bearing point 156.

The crank arms 130 are connected to the prime mover 120 and arerotatable thereby about a crank point 132. The counterweights 136 aredisposed on the crank arms 130. The pitman arms 140 are connectedbetween the first bearing point 156 on the beam 150 and second bearingpoints or wrist pins 134 on the crank arm 130. The second bearing points134 are disposed on the crank arm 130 between the counterweights 136 andthe crank points 132.

The unit 100 includes these and other features similar to thosedisclosed previously with reference to FIG. 2A. In addition to havingthe zero-imbalance beam 150 with the end weight 150, the presentconfiguration is a phased pumping unit where the crank arms 130 aredesigned with the counterweights 136 lagging behind the attachment point(i.e., wrist pins 134) of the pitman arms 140.

A geometric arrangement of the unit 100 is schematically depicted inFIG. 3B. As with the previous arrangement of FIG. 2B, a forward section153 a of the forward end of the beam 150 and the head 152 disposedforward of the pivot point 116 has a forward weight (WF+WH), whereas arearward section 153 b of the rearward end of the beam 159 and the endweight 160 disposed rearward of the pivot point 116 has a rearwardweight (WR+WE). The forward weight (WF+WH) can be balanced relative tothe rearward weight (WF+WE) about the pivot point 116 so that thebenefits of the previous arrangement can be achieved. Accordingly, theweight value (WE) for end weight 160 is selected to achieve this balanceby countering any increased weight from an increased length (A) of theforward beam end and from an increased size for the head 152 so thepumping unit 150 can be used for longer stroke applications.

In contrast to the previous arrangement, the second bearing points orwrist pins 134 are disposed offset at an angle (α) from the longitudinalaxes 131 of the crank arms 130. In particular, the crankpin holes in aconventional pumping unit run parallel to the longitudinal axis 131 ofthe crank arm 130. For this phased unit 100, however, the crankpin holesfor the wrist pin 134 are placed at an offset angle (α) from thelongitudinal axis 131 of the crank arm 130. (The value of the offsetangle (α) depends on the particulars of the implementation, such as thedimensions (e.g., KPRCAGHI) of the unit 100, rod loads, counterweightvalues, etc. In general, the offset angle (α) can be about 5-deg., butcould be between 4-deg. and 15-deg. in most implementations.) Therefore,the counterweights 136 on the crank arms 130 lag behind the pivotconnection (wrist pins 134) between the crank arms 130 and the pitmanarms 140 as the crank arms 130 rotate clockwise. The phased pumping unit100 must rotate clockwise. The length (P+) of the pitman arm 140 may bedifferent than the previous arrangement due to the lagging counterweight(136).

Another geometric arrangement of the unit 100 is schematically depictedin FIG. 3C. This arrangement is similar to those discussed above withreference to FIGS. 2B and 3B. Again, a forward section 153 a of theforward end of the beam 150 and the head 152 disposed forward of thepivot point 116 has a forward weight (WF+WH), whereas a rearward section153 b of the rearward end of the beam 159 and the end weight 160disposed rearward of the pivot point 116 has a rearward weight (WR+WE).The forward weight (WF+WH) can be balanced relative to the rearwardweight (WF+WE) about the pivot point 116 so that the benefits of theprevious arrangement can be achieved. Accordingly, the weight value (WE)for the end weight 160 is selected to achieve this balance by counteringany increased weight from an increased length (A) of the forward beamend and from an increased size for the head 152 so the pumping unit 150can be used for longer stroke applications.

In addition to having the zero-imbalance beam 150 with the end weight160, the present configuration is a phased pumping unit where the crankarms 130 are designed with the counterweights 136 lagging behind theattachment points (i.e., wrist pins 134) of the pitman arms 140. Forexample, similar to the previous arrangements, the second bearing pointor wrist pin 134 is disposed offset at an angle (α) from a longitudinalaxis 131 of the crank arm 130. In particular, the crankpin holes forthis phased unit 100 are placed at an offset angle (α) from thelongitudinal axis 131 of the crank arm 130. Therefore, thecounterweights 136 on the crank arms 130 lag behind the pivot connection(wrist pins 134) between the crank arms 130 and the pitman arms 140 asthe crank arms 140 rotate clockwise. (Again, the offset angle (α) can beabout 5-deg. or between 4-deg. and 15-deg. in most implementations.) Thephased pumping unit 100 must rotate clockwise. The length (P+) of thepitman arm 140 may be different than the previous arrangement due to thelagging counterweight (136).

In contrast to the previous arrangements, the gear reducer 124 for thisunit 100 in FIG. 3B is placed further back from the walking beam pivotpoint (i.e., saddle bearing assembly 116). In other words, the crankpoint of the crankshaft 132 is situated vertically rearward below thebearing point 156 on the beam 150 when the beam 150 is situatedhorizontally. In particular and as noted previously, the gear reducer124 has a slow-speed shaft—i.e., the crankshaft 132 about which thecrank arms 130 rotate. For a conventionally situated reducer, the centerof this slow-speed crankshaft would be situated relative to the unit'sfulcrum point so that the crankshaft may sit directly under the centerof the equalizer bearing shaft. In this phased pumping unit 100,however, the gear reducer 124 is situated further back from the fulcrumpoint 116. Therefore, the slow-speed crankshaft 132 of the gear reducer124 on the phased unit 100 sits rearward of the equalizer bearing 156.The horizontal separation (I+) of the crank point 132 from the fulcrumpoint 116 may be different than the previous arrangement. In otherwords, the horizontal distance (I+) between the saddle bearing 116 andthe crank point 132 is greater than the horizontal distance (C) betweenthe saddle bearing 116 and the equalizing bearing 156. Again, the valuesof these horizontal distances (I+) and (C) depend on the particulars ofthe implementation, such as the other dimensions (e.g., KPRAGH) of theunit 100, rod loads, counterweight values, etc. In general, thehorizontal distance (I+) can be greater in length than the beam'shorizontal distance (C). In other words, the horizontal distance (I+)can be greater than approximately 10%) in length than the beam'shorizontal distance (C). Such an arrangement dictates some of the otherdimensions for the interconnected links (KPRC) of the unit 100.

As the geometries of Figs. Although not explicitly shown, the feature ofthe gear reducer 124 situated further back from the fulcrum point 116(as in FIG. 3B) could be used with crankpin holes that are aligned alongthe longitudinal axis 131 of the crank arm 130 (as in FIG. 2B).

The foregoing description of preferred and other embodiments is notintended to limit or restrict the scope or applicability of theinventive concepts conceived of by the Applicants. It will beappreciated with the benefit of the present disclosure that featuresdescribed above in accordance with any embodiment or aspect of thedisclosed subject matter can be utilized, either alone or incombination, with any other described feature, in any other embodimentor aspect of the disclosed subject matter.

In exchange for disclosing the inventive concepts contained herein, theApplicants desire all patent rights afforded by the appended claims.Therefore, it is intended that the appended claims include allmodifications and alterations to the full extent that they come withinthe scope of the following claims or the equivalents thereof.

What is claimed is:
 1. A surface pumping unit operated by a prime moverfor reciprocating a rod load for a downhole pump in a well, the unitcomprising: a frame disposed at surface and having a fulcrum point; abeam being pivotable at the fulcrum point of the frame, the beam havingfirst and second ends, the first end having a head connecting to the rodload extending from the well, the second end having a first bearingpoint and having an end weight disposed rearward of the first bearingpoint, a forward section of the first end of the beam and the headdisposed forward of the fulcrum point having a forward weight, arearward section of the second end of the beam and the end weightdisposed rearward of the fulcrum point having a rearward weight, theforward weight being balanced relative to the rearward weight; a crankarm connected to the prime mover and rotatable thereby about a crankpoint; a counterweight disposed on the crankarm; and a pitman armconnected between the first bearing point on the beam and a secondbearing point on the crank arm, the second bearing point being disposedbetween the counterweight and the crank point.
 2. The unit of claim 1,wherein the crank arm rotated by the prime mover about the crank pointtranslates the pitman arm to oscillate the beam on the fulcrum point andreciprocates the rod load along the wellbore axis.
 3. The unit of claim1, wherein the frame comprises: a base disposed at the surface; and apost extending from the base to the fulcrum point along a line fromvertical.
 4. The unit of claim 1, wherein the beam defines a straightaxis having first and second sections, the first section from thefulcrum point to a face of the head having a first length (A), thesecond section from the fulcrum point to the first bearing point havinga second length (C); and wherein the first length (A) is greater thanthe second length (C).
 5. The unit of claim 1, wherein the fulcrum pointcomprises a saddle bearing; wherein the first bearing point comprises anequalizer bearing; and wherein the second bearing point comprises acrank pin bearing.
 6. The unit of claim 1, further comprising: anothercrank arm connected to the prime mover and rotatable thereby aboutanother crank point; and another pitman arm connected between anotherfirst bearing point on the beam and another second bearing point on theother crank arm, wherein the pitman arms connect with an equalizer beamat the first bearing point.
 7. The unit of claim 1, further comprising agear reducer operably connecting the crank point to the prime mover. 8.The unit of claim 1, wherein the crank point is centered verticallybelow the first bearing point on the beam when the beam is situatedhorizontally.
 9. The unit of claim 8, wherein the first bearing point isdisposed at a first horizontal dimension (C) along the beam relative tothe fulcrum point; and wherein the crank point is disposed at a secondhorizontal dimension (I) relative to the fulcrum point, the secondhorizontal dimension (I) being approximately equal to the firsthorizontal dimension (C).
 10. The unit of claim 8, wherein the crank armdefines a longitudinal axis, the second bearing point being disposedalong the longitudinal axis of the crank arm.
 11. The unit of claim 8,wherein the crank arm defines a longitudinal axis, the second bearingpoint being disposed offset at an angle from the longitudinal axis ofthe crank arm.
 12. The unit of claim 1, wherein the crank point issituated vertically rearward below the first bearing point on the beamwhen the beam is situated horizontally.
 13. The unit of claim 12,wherein the first bearing point is disposed at a first horizontaldimension (C) along the beam relative to the fulcrum point; and whereinthe crank point is disposed at a second horizontal dimension (I)relative to the fulcrum point, the second horizontal dimension (I) beinggreater than the first horizontal dimension (C).
 14. The unit of claim12, wherein the crank arm defines a longitudinal axis, the secondbearing point being disposed along the longitudinal axis of the crankarm.
 15. The unit of claim 12, wherein the crank arm defines alongitudinal axis, the second bearing point being disposed offset at anangle from the longitudinal axis of the crank arm.
 16. A surface pumpingunit operated by a prime mover for reciprocating a rod load for adownhole pump in a well, the unit comprising: a frame disposed at thesurface and having a fulcrum point; a beam being pivotable at thefulcrum point of the frame, the beam having first and second ends, thefirst end having a head connecting to the rod load extending from thewell, the second end having a first bearing point and having an endweight disposed rearward of the first bearing point; a crank armdefining a longitudinal axis, the crank arm connected to the prime moverand rotatable thereby about a crank point; a counterweight disposed onthe crankarm; and a pitman arm connected between the first bearing pointon the beam and a second bearing point on the crank arm, the secondbearing point being disposed between the counterweight and the crankpoint and being disposed offset at an angle from the longitudinal axisof the crank arm.
 17. The unit of claim 16, wherein a forward section ofthe first end of the beam and the head disposed forward of the pivotpoint having a forward weight, a rearward section of the second end ofthe beam and the end weight disposed rearward of the pivot point havinga rearward weight, the forward weight being balanced relative to therearward weight about the pivot point.
 18. The unit of claim 16, whereinthe crank point is situated vertically rearward below the first bearingpoint on the beam when the beam is situated horizontally.
 19. The unitof claim 18, wherein the first bearing point is disposed at a firsthorizontal dimension (C) along the beam relative to the fulcrum point;and wherein the crank point is disposed at a second horizontal dimension(I) relative to the fulcrum point, the second horizontal dimension (I)being greater than the first horizontal dimension (C).
 20. Areciprocating pump system for a well, the system comprising: a downholepump disposed in the well; and a pumping unit according to claim 1 orclaim 16 disposed at the surface and coupled to the downhole pump by arod string.